Excavator

ABSTRACT

A levelling hydraulic cylinder is connected between the underside of a boom and the intermediate portion of an arm in addition to a hydraulic cylinder for operating the arm. A fluid chamber on the piston rod push-out side of the levelling cylinder is maintained in communication through a tube with fluid chambers on the piston rod push-out side of a pair of hydraulic cylinders for operating the boom while a fluid chamber on the piston rod pull-in side of the levelling cylinder is maintained in communication through another tube with fluid chambers on the piston rod pull-in side of the pair of hydraulic cylinders for operating the boom. A bucket supported at the forward end of the arm can be thrust horizontally forwardly to dig out soil as the arm is oscillated when a piston rod sliding into and out of the hydraulic cylinder for operating the arm.

[ Dec. 23, 1975 EXCAVATOR [75] Inventor: Nobuya Okabe, Ibaraki, Japan[73] Assignee: Hitachi Construction Machinery Co., Ltd., Japan [22]Filed: July 31, 1973 [2]] Appl. No.: 384,299

[30] Foreign Application Priority Data Aug. 28, 1972 Japan 47-85352 [52]US. Cl. 214/763; 214/771; 214/778 [51] Int. Cl. B66F 9/00 [58] Field ofSearch 214/138 R, 761, 762, 763, 214/764, 778, 771

[56] References Cited UNITED STATES PATENTS 3,220,581 1 1/1965 Pedersenet al. 214/764 3,230,717 l/1966 214/771 3,339,763 9/1967 214/7623,465,903 9/1969 Wilson 214/138 R 3,586,182 6/1971 Schwing 214/138 R I-I 8c |||||||l I l 1 8b Primary Examiner-Robert J. Spar AssistantExaminer-Lawrence J. Oresky Attorney, Agent, or Firm-Craig & Antonelli[57] ABSTRACT A levelling hydraulic cylinder is connected between 1 theunderside of a boom and the intermediate portion of an arm in additionto a hydraulic cylinder for operating the arm. A fluid chamber on thepiston rod pushout side of the levelling cylinder is maintained incommunication through a tube with fluid chambers on the piston rodpush-out side of a pair of hydraulic cylinders for operating the boomwhile a fluid chamber on the piston rod pull-in side of the levellingcylinder is maintained in communication through another tube with fluidchambers on the piston rod pull-in side of the pair of hydrauliccylinders for operating the boom. A bucket supported at the forward endof the arm can be thrust horizontally forwardly to dig out soil as thearm is oscillated when a piston rod sliding into and out of thehydraulic cylinder for operating the arm.

13 Claims, Drawing Figures m" 3 "30 I7 '1 15 A 23 My. ---29 'JF- g l I34 1 19 I61 26 111!- L 27 "1,, I V 28 11 I 2| U.S. Patient Dec.23, 1975Sheet10f3 3,927,781

FIG. I

PRIOR ART US. Patent Dec. 23, 1975 FIG. 3

Sheet 2 of 3 US. Patent Dec. 23, 1975 Sheet 3 of3 3,927,781

FIG. 4

PRIOR ART FIG. 5

EXCAVATOR BACKGROUND OF THE INVENTION 1. Field of the Invention Thisinvention relates to an excavator of the type which is provided with abucket for digging out soil supported at one end of an arm in turn issupported by a boom connected to an excavator proper so that the bucketcan be pushed out horizontally forwardly by means of the boom and thearm to dig out soil.

2. Description of the Prior Art In the excavator of the type described,it has hitherto been customary to mount an arm 1 at the foward end of aboom 2 for pivotal movement, and a bucket 3 is supported at the forwardend of the arm 1 for pivotal movement as shown in FIG. 1. The operationof digging out soil and dumping the soil into a truck performed by aconventional excavator is such that the bucket 3 initially disposed nearan excavator proper 4 in a position designated I is pushed outhorizontally forwardly from position I to a position designated II. Whenthe bucket 3 is in this position, the front end of the bucket 3 is movedupwardly and the rear end thereof is moved downwardly so that the bucket3 moves to a position designated III to scoop up soil. When the bucket 3is disposed in this position, the boom 2 is moved to an upright positionso that the bucket 3 is moved to a position designated IV. When thebucket 3 is in this position, the rear end of the bucket 3 is movedupwardly and the front end thereof is moved downwardly so that the soilin the bucket is dumped into the truck for transportation. The movementsof the bucket 3, arm 1 and boom 2 are controlled by hydraulic cylinders5., 6 and 7 respectively connected to these parts as shown in FIG. 1.

Of all the movements of the parts described above, the horizontalforward movement of the bucket 3 for scooping up soil and dumping thesoil in the bucket into the truck can be performed adequately only ifthe boom 2, arm 1 and bucket 3 are simultaneously operated so that eachof them moves a proper distance in a proper direction. This makes itnecessary for the operator to operate the plurality of hydrauliccylinders 5, 6 and 7 at a time when the bucket 3 is to be pushed outhorizontally forwardly as aforementioned. Thus, conventional excavatorshave the disadvantage of their operators having to be highly skilled inthe art of operating their machines. An added disadvantage is that evenskilled operators get greatly tired when they operate their machines topush out the bucket 3 horizontally forwardly.

SUMMARY OF THE INVENTION This invention obviates the aforementioneddisadvantages of conventional excavators of the bucket type in which thebucket is pushed out horizontally forwardly. Accordingly, the inventionhas as its object the provision of an excavator of the bucket type whichcan be operated with greater ease and which permits an excavatingoperation to be performed with a higher degree of efficiency.

According to the invention, there is provided an excavator of the buckettype comprising an excavator proper including a movable body, a rotarybody and a swivel body, a boom pivotally supported at a forward endportion of the swivel body of the excavator proper for movement betweena lying position and an upright position, a pair of hydraulic cylindersfor moving the boom between the lying position and upright position, anarm pivotally supported through a pin at a forward end of the boom foroscillating motion, a hydraulic cylinder for operating the arm andcausing the same to move in oscillating motion, a bucket pivotallysupported at a forward end of the arm, a hydraulic cylinder foroperating the bucket pivotally connected through a pair of rigid linksto a forward end portion of the arm for moving the bucket horizontallyforwardly away from the excavator proper in oscillating motion, and alevelling hydraulic cylinder connected at one end to the boom at itsunderside and at the other end to the arm at its substantiallyintermediate portion, said levelling hydraulic cylinder having a fluidchamber on its piston rod push-out side maintained in communicationthrough a tube with a fluid chamber on the piston rod push-out side ofeach hydraulic cylinder for operating the boom and another fluid chamberon its piston rod pull-in side maintained in communication throughanother tube with a fluid chamber on the piston rod pullin side of eachhydraulic cylinder for operating the boom whereby the bucket can bepushed out horizontally forwardly as the arm is moved in oscillatingmotion by the action of the hydraulic cylinder for operating the arm.

One of the features of the invention is that the bucket can be pushedout horizontally forwardly merely by manipulating the hydraulic cylinderfor operating the arm.

Other and additional objects and features of the invention will becomeevident from the description set forth hereinafter when considered inconjunction with the accompanying drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 schematically shows a conventionalexcavator of the bucket type in which the bucket is pushed outhorizontally forwardly;

FIG. 2 is a schematic view of the excavator of the bucket typecomprising one embodiment of the invention;

FIG. 3 is a view in explanation of the operation of excavator accordingto the invention;

FIG. 4 shows the relation between the digging force and the reaction atwork when soil digging is carried out by the conventional excavatorshown in FIG. 1; and

FIG. 5 shows the relation between the digging force and the reaction atwork when soil digging is carried out by the excavator according to theinvention.

DESCRIPTION OF A PREFERRED EMBODIMENT The excavator according to theinvention will now be described with reference to the preferredembodiment shown in the drawings.

In FIG. 2, 8 generally designates an excavator proper according to theinvention including a movable body 8a having a caterpillar, a rotarybody 8b mounted on the movable body 8a, and a swivel body mounted on therotary body 8b. The swivel body 8c is provided with an operators cab 8d.

A boom 9 is pivotally connected to the swivel body 8c for movement inone vertical plane between a lying position and an upright position bythe action of a pair of hydraulic cylinders 10, 10 for operating theboom 9. The hydraulic cylinders 10, 10 are each disposed on one ofopposite sides of the boom 9 and connected at its base to the swivelbody 80 through a pin 11. Piston rods 12, 12 each received in one of thepair of hydraulic cylinders 10, are connected to the boom 9 through apin 13. 7

An arm 15 is pivotally connected through a pin 14 to a forward end ofthe boom 9 for movement in one vertical plane, like the boom 9, by theaction of a hydraulic cylinder 16 for operating the arm 15. Thehydraulic cylinder 16 is connected at its base through a pin 17 to abracket 18 projecting downwardly from the underside of a forward endportion of the boom 9. The hydraulic cylinder 16 receives therein apiston rod 19 connected at its forward end to a forward end portion ofthe arm 15 through a pin 20.

A bucket 21 is connected through a pin 22 to the forward end of the arm15 and moves in what is referred to as a wrist motion by the action of ahydraulic cylinder 23 for operating the bucket 21. The hydrauliccylinder 23, which is connected at its base through a pin 24 to theforward end portion of the boom 9, receives therein a piston rod 25connected at its forward end through a pin 26 to one end of each ofrigid links 27 28. The rigid links 27, 28 are connected at the other endto the forward end of the piston rod 19 received the hydraulic cylinder16 respectively.

A levelling hydraulic cylinder 29 operatively associated with thehydraulic cylinder 16 for operating the arm 15 is connected between theboom 9 and the arm 15 and disposed nearer to them than the hydrauliccylinder 16, so that the levelling hydraulic cylinder 29 can move intothe arm 15. More specifically, the levelling hydraulic cylinder 29 is.connected at its base through a pin 30 to the bracket 18 projectingdownwardly from the underside of the forward end portion of the boom 9and receives therein a piston rod 31 connected through a pin 32 to theunderside of the substantially intermediate portion of the arm 15.

The levelling hydraulic cylinder 29 has a fluid chamber on the pistonrod push-out side thereof which is maintained through a tube 33 incommunication with fluid chambers on the piston rod push-out side of thehydraulic cylinders 10, 10, and another fluid chamber on the piston rodpull-in side thereof which is maintained through another tube 34 incommunication with fluid chambers on the piston rod pull-in side of thehydraulic cylinders'10, 10.

The connections between the levelling hydraulic cylinder 29 and thehydraulic cylinders 10, 10 perform an important function in pushing outthe bucket 21 horizontally outwardly. More specifically, when the arm 15is pivoted in the direction of an arrow A in FIG. 2 by the action of thehydraulic cylinder 16, the piston rod 31 is forced to slide out of thelevelling hydraulic cylinder 29. This results in the fluid underpressure in the fluid chamber on the piston rod pull-in side of thelevelling hydraulic cylinder 29 being forced to flow out of the fluidchamber and moving through tube 34 into the fluid chambers on the pistonrod pull-in side of the hydraulic cylinders 10, 10. This in turn resultsin the fluid under pressure in the fluid chambers on the piston rodpush-out side of the hydraulic cylinders 10, 10 returning through tube33 to the fluid chamber on the piston rod push-out side of the levellinghydraulic cylinder 29. This causes the boom 9 to move to the lyingposition.

If the arm 15 is pivoted in a direction opposite to the direction of thearrow A, the boom 9 can be moved to the upright position. The hydrauliccylinders 10, 10 and 29 are constructed such that they are equal to eachother in the diameter of their piston and piston rod or in the pressurereceiving area ratio in order to prevent the occurrence of a vacuum dueto the oversupply or the lack of fluid when the aforementioned operationis performed.

The position in which the base of the hydraulic cylinder 23 is connectedto the boom 9 through pin 24 is selected such that a quadrilateral isformed by the pins 14, 20, 26 and 24 in the plane of FIG. 2, so that atoothed portion 21a of the bucket 21 can be maintained at apredetermined angle with respect to the horizontal when the arm 15 isoscillated and the boom 9 is moved between the lying and uprightpositions. The hydraulic cylinders l0, l6 and 23 can be actuatedindependently of one another by manipulating control levers provided inthe operators cab 8d.

In operation, fluid under pressure is supplied to a fluid chamber on thepiston rod push-out side of the hydraulic cylinder 16 for operating thearm 15 when the bucket 21 is disposed in a position designated V inwhich it is near the excavator proper 8 as shown in FIG. 2. This resultsin the piston rod 19 sliding out of the cylinder 16 and causing the arm15 to pivot in the direction of the arrow A about the pin 14 at theforward end of the boom 9. As a result, the piston rod 31 is forced toslide out of the levelling hydraulic cylinder 29, and the fluid underpressure in the fluid chamber on the piston rod pull-in side of thelevelling hydraulic cylinder 29 flows into the fluid chamber on thepiston rod pull-in side of each hydraulic cylinder 10 through tube 34 tooperate the boom 9. This results in the piston rod 12 sliding into therespective hydraulic cylinder 10, so that the boom 9 moves into thelying position. Thus, the bucket 21 is pushed out horizontally forwardlyaway from the excavator proper 8 into a position designated VI in FIG. 3while its toothed portion 21a is maintained in the horizontal positionby the quadrilateral formed by the pins 24, 20, 26 and 24. By moving thebucket 21 from this position into a position designated VII in which thefront end of the bucket is disposed at a higher level than its rear end,soil can be dug out by the bucket 21 and held therein.

When it is desired to move the bucket 21 toward the excavator proper 8,the operator has only to cause the piston rod 19 to slide into thehydraulic cylinder 16 for operating the arm 15 by supplying fluid underpressure to a fluid chamber on the piston rod pull-in side of thehydraulic cylinder 16.

By merely manipulating the hydraulic cylinder 16 alone, it is possibleto push out the bucket 21 horizontally forwardly away from the excavatorproper 8 to dig out soil. Also, by moving horizontally forwardly thebucket 21 containing therein the scooped soil from a dash-and-dot lineposition designated VIII to a dashand-dot line position designated IX inFIG. 3, it is possible to move the bucket 21 to a position in which thecontents of the bucket 21 can be dumped into a truck.

When it is desired to move the boom 9 to the upright position by causingthe piston rods 12, 12 to slide out of the hydraulic cylinders 10, 10 asthe bucket 21 is pushed out horizontally outwardly away from theexcavator proper 8 to a maximum as shown in FIG. 3, fluid under pressureis caused to act on the fluid chambers on the piston rod push-out sideof the hydraulic cylinders l0, 10. The fluid under pressure caused toact on the fluid chambers on the piston rod push-out side of thehydraulic cylinders 10, 10 in this way may act on the fluid chamber onthe piston rod push-out side of the hydraulic cylinder 29 through tube33. This causes no trouble because the hydraulic cylinder 16 foroperating the arm 15 is locked at this time.

The excavator according to the invention is constructed such that theforce with which the bucket is 'rushed out horizontally forwardly awayfrom the excavator proper in digging out soil is greater than the forcewith which the bucket of a conventional excavator is pushed out in thesame direction, so that soil digging can be carried out with a higherdegree of efficiency. Generally, a reaction to the force with whichdigging is carried out is produced at the toothed portion of the bucketwhen the bucket is pushed out horizontally forwardly and its front endis raised to a higher level than its rear end when an earth diggingoperation is performed. If a reaction F1 to the force with which earthdigging is carried out is produced at the toothed portion of the bucket3 of a conventional excavator as shown in FIG. 4, the reaction F1 and aforce P produced by the hydraulic cylinder 6 for operating the arm willbalance as follows.

P I= F1 m (1) where l is the distance between the point at the forwardend of the boom 2 at which the arm 1 is pivotally supported at its baseand the hydraulic cylinder 6 for operating the arm 1, and m is thedistance between the point at the forward end portion of the boom 2 atwhich the arm 1 is pivotally supported at its base and the point atwhich the reaction F1 is produced. From formula (1), the reaction F1 canbe rewritten as follows:

7 F1 l/m P (2) If a reaction F2 to the force with which earth digging iscarried out is produced at the toothed portion 21a of the bucket 21 ofthe excavator according to the invention as shown in FIG. 5, thereaction F2 and a force Q exerted by thelevelling hydraulic cylinder 29in operation will balance as follows:

Pl'+Q-n'-F2'm' (3) where l is the distance between the point 14 at theforward end portion of the boom 9 at which the arm 15 is pivotallysupported at its base and the hydraulic cylinder. 16, n is the distancebetween the pivot 14 and the levelling hydraulic cylinder 29, and m isthe distance between the pivot 14 and the point at which the reaction F2is produced. From formula (3), the reaction F2 can be rewritten asfollows:

Thus, the reaction F2 is greater than the reaction F1 in the prior artby (n'/m') Q.

The force exerted by the levelling hydraulic cylinder 29 may be eitherpositive or negative. The force Q is positive when the working angle 0of the reaction F2 produced at the toothed portion 21a of the bucket 21is such that the reaction F2 acts from above on the surface of thetoothed portion 21a; the force Q is negative when the working angle 0 ofthe reaction F2 produced at the toothed portion 210 of the bucket 21 issuch that the reaction acts from below on the surface of the toothedportion 21a. If the working angle 0 of the reaction F2 is positive, thehydraulic cylinders 10, 10 for operating the boom 9 will be subjected toa force which will tend to cause the piston rods 12, 12 to slide intothe respective cylinders 10, 10. Thus, a pressure will be produced inthe fluid chambers on the piston rod pushout side of the cylinders 10,10 and transmitted through tube 33 to the levelling hydraulic cylinder29 where a pressure will be produced in the fluid chamber on the pistonrod push-out side thereof, thereby causing the piston rod 31 to slideout of the levelling hydraulic cylinder 29. When the working angle 0 ofthe reaction F2 is negative an operation reversed to the aforementionedoperation will be performed.

When an earth digging operation is performed, the working angle 0 of thereaction F2 is positive in most cases and the excavator according to theinvention exerts a greater digging force than a conventional excavatorby (n'lm') Q. When the working angle 0 is negative, however, the diggingforce exerted by the excavator according to the invention is reduced asmuch. This offers an advantage in that the excavator proper is kept fromslipping because at this time it is subjected to an upwardly orientedforce and its ground gripping force is reduced in magnitude.

From the foregoing description, it will be appreciated that theinvention is characterized by the provision, in addition to thehydraulic cylinder for operating the arm, of the levelling,hydrauliccylinder between the boom and the arm. Such levelling hydraulic cylinderbeing constructed such that its fluid chambers are maintained incommunication with corresponding fluid chambers in the hydrauliccylinders for operating the boom, so that the bucket supported at theforward end of the arm can be pushed out horizontally outwardly awayfrom the excavator proper merely by manipulating the hydraulic cylinderfor operating the arm. By virtue of this feature, the invention offersmany advantages. Operation of the excavator is facilitated, fatigue ofthe operator is greatly lessened and operation efficiency is greatlyincreased. The invention permits the bucket to be pushed outhorizontally outwardly with a greater force in digging out soil, so thatthe ability of the excavator to dig out soil can be greatly enhanced.The embodiment shown and described herein has a link ratio such that thecapacity of the excavator can be increased by 30 percent.

What I claim is:

1. An excavator of the bucket type comprising an excavator properincluding movable body means, rotary body means and swivel body means,boom means pivotally supported at a forward end portion of said swivelbody means of the excavator proper for movement between a lying positionand an upright position, boom hydraulic cylinder means for moving theboom means, arm means pivotally supported at a forward end of said boommeans for oscillating motion, arm hydraulic cylinder means for operatingsaid arm means, bucket means pivotally supported at a forward end ofsaid arm means, bucket hydraulic cylinder means for operating saidbucket means pivotally connected through linking means to an end portionof said arm means for moving the bucket means horizontally forwardlyaway from the excavator proper in oscillating motion, and levellinghydraulic cylinder means connected at one end to the boom-means and atanother end to the arm means, said levelling hydraulic cylinder meanshaving a first fluid chamber on a piston rod push-out side thereofmaintained in fluid communication with a fluid chamber on a piston rodpush-out side of the boom hydraulic cylinder means for operating theboom means, said levelling hydraulic cylinder means also having a secondfluid chamber on a piston rod pull-in side maintained in fluidcommunication with a 7 fluid chamber on a piston rod pull-in side of theboom hydraulic cylinder means for operating the boom means whereby thebucket means can be pushed out horizontally forwardly as the arm meansis moved in oscillating motion by the action of the arm hydrauliccylinder means.

2. An excavator according to claim 1 wherein said levelling hydrauliccylinder means and said boom hydraulic cylinder means are constructedsuch that they are equal to each other in the diameter of their pistonand piston rod or in the pressure receiving area ratio in order toprevent the occurrence of a vacuum due to the oversupply or the lack offluid when the bucket means is pushed horizontally outwardly from theexcavator proper.

3. An excavator according to claim 1 wherein said linking means includesa pair of rigid links, and wherein said pair of rigid links arepivotally connected at one end through a pin to a forward end of apiston rod received in said bucket hydraulic cylinder means and anotherend of one of said pair of rigid links is pivotally connected throughanother pin to a forward end portion of said arm means while the otherend of the other rigid link is pivotally connected to the bucket means.

4. An excavator according to claim 3 wherein said bucket hydrauliccylinder means is pivotally connected at its base through a pin to saidboom means, so that said pin for pivotally connecting the base of buckethydraulic cylinder means to said boom means, a pin for pivotallysupporting the arm means at the forward end of the boom means, said pinfor pivotally connecting one end of one of said pair of rigid links tothe forward end of the piston rod received in said bucket cylindermeans, and said pin for pivotally connecting the other end of said oneof said pair of rigid links to the front end portion of said arm meansform a quadrilateral whereby a toothed portion of said bucket means canbe maintained at a predetermined angle with respect to the horizontalwhen the boom means is moved between the lying and upright positions andthe arm means is moved in oscillating motion.

5. An excavator according to claim 4 wherein said boom hydrauliccylinder means, said arm hydraulic cylinder means, and said buckethydraulic cylinder means can be operated independently of one another bymanipulating control levers provided in an operators cab in said swivelbody of said excavator proper.

6. An excavator according to claim 1, wherein the boom means is movablebetween a lying position and an upright position, and wherein the armmeans is movable in oscillating motion.

7. An excavator according to claim 6, wherein the boom hydrauliccylinder means comprises a pair of hydraulic cylinders, and wherein thearm means is pivotally supported to the boom means through a pin.

8. An excavator according to claim 7, wherein the linking meanscomprises a pair of rigid links.

9. An excavator according to claim 1, wherein the levelling hydrauliccylinder means is connected at the underside of the boom means and at anintermediate portion of the arm means.

10. An excavator according to claim 9, wherein said first and secondfluid chambers are in fluid communication with corresponding fluidchambers of a common boom hydraulic cylinder means.

11. An excavator according to claim 1, wherein the boom hydrauliccylinder means and the arm hydraulic cylinder means are arranged suchthat the bucket means is forced outwardly from the body means with anincreased force in response to increased resistance forces experiencedby the bucket means which forces tend to move the boom means toward alying position.

12. An excavator according to claim 10, wherein said first and secondfluid chambers are in fluid communication with corresponding fluidchambers of each boom hydraulic cylinder means.

13. An excavator according to claim 1, wherein the boom hydrauliccylinder means and the arm hydraulic cylinder means are arranged suchthat the bucket means experiences a reduced outward movement force inresponse to increased resistance forces experienced by the bucket meanswhich forces tend to move the boom means toward an upright position.

1. An excavator of the bucket type comprising an excavator properincluding movable body means, rotary body means and swivel body means,boom means pivotally supported at a forward end portion of said swivelbody means of the excavator proper for movement between a lying positionand an upright position, boom hydraulic cylinder means for moving theboom means, arm means pivotally supported at a forward end of said boommeans for oscillating motion, arm hydraulic cylinder means for operatingsaid arm means, bucket means pivotally supported at a forward end ofsaid arm means, bucket hydraulic cylinder means for operating saidbucket means pivotally connected through linking means to an end portionof said arm means for moving the bucket means horizontally forwardlyaway from the excavator proper in oscillating motion, and levellinghydraulic cylinder means connected at one end to the boom means and atanother end to the arm means, said levelling hydraulic cylinder meanshaving a first fluid chamber on a piston rod push-out side thereofmaintained in fluid communication with a fluid chamber on a piston rodpush-out side of the boom hydraulic cylinder means for operating theboom means, said levelling hydraulic cylinder means also having a secondfluid chamber on a piston rod pull-in side maintained in fluidcommunication with a fluid chamber on a piston rod pull-in side of theboom hydraulic cylinder means for operating the boom means whereby thebucket means can be pushed out horizontally forwardly as the arm meansis moved in oscillating motion by the action of the arm hydrauliccylinder means.
 2. An excavator according to claim 1 wherein saidlevelling hydraulic cylinder means and said boom hydraulic cylindermeans are constructed such that they are equal to each other in thediameter of their piston and piston rod or in the pressure receivingarea ratio in order to prevent the occurrence of a vacuum due to theoversupply or the lack of fluid when the bucket means is pushedhorizontally outwardly from the excavator proper.
 3. An excavatoraccording to claim 1 wherein said linking means includes a pair of rigidlinks, and wherein said pair of rigid links are pivotally connected atone end through a pin to a forward end of a piston rod received in saidbucket hydraulic cylinder means and another end of one of said pair ofrigid links is pivotally connected through another pin to a forward endportion of said arm means while the other end of the other rigid link ispivotally connected to the bucket means.
 4. An excavator according toclaim 3 wherein said bucket hydraulic cylinder means is pivotallyconnected at its base through a pin to said boom means, so that said pinfor pivotally connecting the base of bucket hydraulic cylinder means tosaid boom means, a pin for pivotally supporting the arm means at theforward end of the boom means, said pin for pivotally connecting one endof one of said pair of rigid links to the forward end of the piston rodreceived in said bucket cylinder means, and said pin for pivotallyconnecting the other end of said one of said pair of rigid links to thefront end portion of said arm means form a quadrilateral whereby atoothed portion of said bucket means can be maintained at apredetermined angle with respect to the horizontal when the boom meansis moved between the lying and upright positions and the arm means ismoved in oscillating motion.
 5. An excavator according to claim 4wherein said boom hydraulic cylinder means, said arm hydraulic cylindermeans, and said bucket hydraulic cylinder means can be operatedindependently of one another by manipulating control levers provided inan operator''s cab in said swivel body of said excavator proper.
 6. Anexcavator according to claim 1, wherein the boom means is movablebetween a lying position and an upright position, and wherein the armmeans is movable in oscillating motion.
 7. An excavator according toclaim 6, wherein the boom hydraulic cylinder means comprises a pair ofhydraulic cylinders, and wherein the arm means is pivotally supported tothe boom means through a pin.
 8. An excavator according to claim 7,wherein the linking means comprises a pair of rigid links.
 9. Anexcavator according to claim 1, wherein the levelling hydraulic cylindermeans is connected at the underside of the boom means and at anintermediate portion of the arm means.
 10. An excavator according toclaim 9, wherein said first and second fluid chambers are in fluidcommunication with corresponding fluid chambers of a common boomhydraulic cylinder means.
 11. An excavator according to claim 1, whereinthe boom hydraulic cylinder means and the arm hydraulic cylinder meansare arranged such that the bucket means is forced outwardly from thebody means with an increased force in response to increased resistanceforces experienced by the bucket means which forces tend to move theboom means toward a lying position.
 12. An excavator according to claim10, wherein said first and second fluid chambers are in fluidcommunication with corresponding fluid chambers of each boom hydrauliccylinder means.
 13. An excavator according to claim 1, wherein the boomhydraulic cylinder means and the arm hydraulic cylinder means arearranged such that the bucket means experiences a reduced outwardmovement force in response to increased resistance forces experienced bythe bucket means which forces tend to move the boom means toward anupright position.